During the last few decades an intensive effort has been made to discover new, clinically useful antimicrobial compositions. Although more than a thousand antibiotics have been discovered, few are found to be of significant antimicrobial use. To be useful an an antimicrobial agent, a substance must have a low toxicity for host cells and a high toxicity for the disease causing microorganism. In other words, the antimicrobial agent must posion the parasite and cause little or no damage to the cells of the host. It is for this reason that a substantial number of the known antimicrobials are unsatifactory. In other words, they are not selective in their action on cells and thus interfere with natural mammaliam or plant defense mechanisms. Certain disease causing microorganisms remain serious problems and some of the major antimicrobials have considerable drawbacks in terms of limited antimicrobial spectrum or serious side effects. These factors necessitate a continuing search for new antimicrobial agents.